Electric fuze for shaped-charge missiles

ABSTRACT

An electric fuze for a shaped-charge missile, said missile having an outer and an inner front closure plate, said plates being spaced apart by an air gap, a tubular stand-off member projecting forwardly from said front closure plates and comprising an outer and an inner tube spaced by an air gap, said tubes being mechanically and electrically connected to different ones of said outer and inner front closure plates, a piezoelectric crystal element being located behind said front closure plates and connected in a circuit comprising an electric fuze, said front closure plates, said tubes and said air gaps, so that initiation of the fuze occurs when the front portion of the missile is deformed and one or both of said air gaps is shortcircuited and said piezoelectric crystal generates an electric pulse.

United States Patent Aronsson et al.

[ 1 June 6,1972

nell, both of Eskilstuna; Ulf W. Molitor, Torshalla, all of Sweden [73] Assignee: Forsvarets Fabriksverke, Eskilstuna,

Sweden [22] Filed: July 24, 1969 [21] Appl. No.: 844,554

Related US. Application Data [63] Continuation-in-part of Ser. No. 686,068, Nov. 28,

3,373,687 3/l968 Simmons l02/56 FOREIGN PATENTS OR APPLICATIONS 909,549 10/ l 960 Great Britain lO2/70.2

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Daniel Bent AnorneyMunson & Fiddler [57] ABSTRACT An electric fuze for a shaped-charge missile, said missile having an outer and an inner front closure plate, said plates being spaced apart by an air gap, a tubular stand-off member projecting forwardly from said front closure plates and comprising an outer and an inner tube spaced by an air gap, said tubes being mechanically and electrically connected to different ones of said outer and inner front closure plates, a piezoelectric crystal element being located behind said front closure plates and connected in a circuit comprising an electric fuze, said front closure plates, said tubes and said air gaps, so that initiation of the fuze occurs when the front portion of the missile is deformed and one or both of said air gaps is short-circuited and said piezoelectric crystal generates an electric pulse.

1 Claim, 1 Drawing Figure ELECTRIC FUZE FOR SHAPED-CHARGE MISSILES This is a continuation-in-part of co-pending application Ser. No. 686,068 filed Nov. 28, 1967.

DESCRIPTION To obtain desired bursting effect with shaped-charge missiles on targets of irregular shape, for example targets which are protected by a wire net, it is desirable that the missile should be brought to detonate also if it hits the target with another part than its foremost front point.

In order to solve this problem it is common to provide the front part of the missile with two caps which are insulated from each .other. When the missile hits the target, the outer cap will be deformed and make contact with the inner cap.

Thereby a current path will be closed. Usually, a capacitor which has been charged at the firing moment will then be discharged through an electrical ignitor, which ignites the explosive charge. The capacitor may for example be charged during the initial acceleration of the missile by means of a piezoelectric crystal as described in the Swedish Pat. specification No. 190,152 (corresponding to Gennan Pat. specification No. 1,145,522 and British Pat. specification No. 909,549).

The major disadvantage of this arrangement is the severe requirements of the insulation between the two caps. A poor insulation may cause the charge in the capacitor to leak away during the flight of the missile towards the target.

The problem of insulation will be avoided if the electrical ignition energy is generated by means of a piezoelectric crystal when themissile hits the target. In known missiles of that kind the effective area of sensitivity of the fuze is, however, limited to a narrow portion at the foremost point of the missile. If that area is increased over the whole caliber of the missile, there will be a very poor trajectory safety, so that there is a risk that the missile will detonate when it passes a tree branch or a protecting grid, which camouflages the weapon from which the missile has been fired.

By means of an arrangement according to the present invention the said disadvantages are avoided. The invention relates to an electric fuze with a trajectory safety device for a shapedcharge missile, in which the missile is provided with a stand off member comprising a tubular sleeve projecting forwards from the envelope of the missile, in order to obtain detonation of the missile ata suitable stand off distance from the target, and in which a front closure plate constitutes the front end wall of the envelope of the missile, said front closure plate having a plain or slightly conical surface which is substantially perpendicular to the longitudinal axis of the missile.

The device according to the invention is mainly characterized therein, that the tubular sleeve comprises two concentric, electrically conducting tubes which are insulated from each other by means of an air gap, the outer tube forming a continuation of an outer, electrically conducting front closure plate, and the inner tube forming a continuation of an inner, electrically conducting front closure plate, said air gap between the tubes having a continuation located between said front closure plates, the inner front closure plate being in mechanical and electrical contact with one side of a number of piezoelectric crystal elements, the other sides of said elements being supported by an electrically conducting annular disc which is mechanically supported but electrically insulated from the envelope of the missile, and in which said crystal elements are electrically connected to a fuze for the shapedcharge of the missile in series with the air gap between said tubes and said front closure plate.

An embodiment of the device according to the present invention will be described in the following, reference being had to the accompanying drawing, which illustrates a longitudinal section through an aerodynamically stabilized, shaped-charge missile according to the invention.

The missile illustrated in the drawing is of the type which is provided with a stand off or remote fuze comprising a tubular sleeve projecting forwards from the envelope of the missile, in

order to bring the missile to detonate at a suitable stand off distance from the target, so that a favorable explosion effect of the shaped-charge is obtained. The missile has a front closure plate constituting the front end wall of the envelope of the missile, said front closure plate having a plain or slightly conical surface, so as to be coincident to or to make an acute angle with a surface which is perpendicular to the longitudinal axis of the missile. The tubular sleeve comprises two concentrical, electrically conducting tubes 1, 2, which are insulated from each other by means of an air gap, the outer tube 1 being a continuation of an outer front closure plate 3, and the inner tube 2 being a continuation of an inner front closure plate 4, said front closure plates being electrically conducting but insulated from each other by means of an air gap which is a continuation of the air gap between said tubes 1 and 2. The inner front closure plate 4 is mechanically and electrically connected with the one side of a number of piezoelectric crystal elements 5. The other sides of said crystal elements are supported by an electrically conducting, annular disc 6 which is mechanically supported by but electrically insulated from the envelope of the missile. The crystal elements are electrically connected in series with the air gaps between the tubes 1, 2 and the front closure plates 3, 4 to a fuze 7 for the explosive charge of the missile which is enclosed in a shell 16. The outer tube is provided with a conical cap or ogive 8.

The path for the current from the piezoelectric elements will be: The front surfaces of the crystal elements 5-the inner front closure plate 4 and the innermost tube 2-the air gap between the front closure plates and the tubes-the outer front closure plate 3 and the outer tube l-the shell 16 of the missile-the fuze 7the tube I0 through the explosive chargethe liner 1 l for the explosive shaped-charge-the annular disc 6the rear surfaces of the crystal elements 5.

The shell 16 has the general shape of a cylinder and is open at its front end. Near the open end the shell 16 has a cylindrical collar I7 which is provided with an outside threading l8 and an inside threading 19.

The outer front closure plate 3 has a rearwardly directed collar portion 20 which has an inside threading 21 by means of which it is threaded on to the threading 18 of the cylindrical collar 17. Thereby, the outer front closure plate 3 is firmly kept to the missile and electrically connected to the shell 16.

An annular insulating member 22 is fitted into the cylindrical collar 17 and resting on a shoulder portion 23 from which the collar 17 projects. The annular insulating member 22 has an inner shoulder portion 24 against which the ring-shaped metal member 6 rests. Between said ring-shaped member 6 and the surface of said shoulder portion 24, the annular edge of the liner ll of the shaped charge is interposed. Thereby, said liner 1 l is electrically connected to the ring-shaped member 6 but insulated from the shell 16. In front of the ringshaped member 6 there are the piezoelectric elements 5 located. In front of said piezoelectric elements 5, and in electrical contact with said elements, the inner front closure plate 4 is placed. The front closure plate 4, the piezoelectric elements, the ring-shaped member 6 and the annular edge of the liner 11 are all kept in place by a threaded annular member 26 of insulating material, which is threaded into the upper part of the insulating, annular member 22. In this way, the piezoelectric elements 5 are electrically insulated from the shell 16 but connected as described in the foregoing to the ring-shaped disc 6 and the inner front closure plate 4.

By an arrangement according to the invention ignition will be obtained also for oblique hits and hits against a protecting grid. If a conventional missile with piezoelectric crystal elements strikes against a tree branch or a bush there will be a sufiicient energy generated to bring about initiation of the fuze but in the device according to the present invention there is an air gap between the tubes and between the front closure plates and, therefore, no initiation of the fuze will take place. By this means, a trajectory safety device is obtained. The air gap will be short-circuited only when the missile strikes against the target whereby ignition of the explosive charge will be obtained.

Between the outer front closure plate 3 and the inner front closure plate 4, there is located a member 14, pivoted for example about an axis 13 which may be welded to the underside of the outer front closure plate 3, which may be actuated from the outside by means of a part 12 projecting through an opening in the outer front closure plate 3. Said member 14 can be moved from the position shown in full lines, wherein the member does not make contact with the inner front closure plate 4, to the position shown in phantom lines, where the bottom part of the member 14 contacts with the inner front closure plate 4 and thus electrically connects the inner front closure plate to the outer front closure plate 3.

The member 14 can be actuated or put into its active position shown in fantom lines, if the operator of the weapon is firing against a target with a low resistance, and if he is convinced that no trajectory safety device is required. In that case, the projectile has the greatest degree of sensitivity.

The sensitivity degree of the ignition device is determined partly by the size of the outer tube and the outer front closure plate and partly of the ratio of the electrical impedance of the fuze and the total electrical capacity of the electrical system. The said total capacity may be continuously varied by means of the conical cap 8 provided at the front end of the outer tube I. Said cap is displaceable in the longitudinal direction of the missile, for example by means of a threading, and is so arranged, that by displacing of the same the capacity between the outer tube 1 and the inner tube 2 will be varied. In dependence of the magnitude of said capacity, more or less of the energy which is generated by the crystal elements when the missile hits the target will be supplied to the fuze. If a certain threshold value of said energy for ignition is exceeded, the explosive charge will detonate. When a fired missile is adjusted to its lowest sensitivity degree, the capacity should have its lowest value. Initiation of the fuze will then take place when the tube 1 or the outer front closure plate 3 has been deformed so much, that the air gap is eliminated or short circuited. Thus, the rigidity of those parts of the missile determine the lowest sensitivity degree.

What we claim is:

I. An electric fuze for an explosive missile having a trajectory safety device; a stand-ofi' member projecting forwardly from said missile; said stand-oil member comprising, an outer tubular member electrically and mechanically connected to an outer front closure plate forming an outer front surface of said missile; an inner tubular member located inside said outer tubular member but spaced apart and electrically insulated therefrom by an air gap; said inner tubular member being connected to an inner front closure plate located behind said outer front closure plate but spaced apart and electrically insulated therefrom by an air gap; said stand-ofimember being of less diameter than said front closure plate from which it projects, whereby said front closure plate forms a shoulder portion to said stand-off member; a set of piezoelectric elements located behind said inner front closure plate, and mounted to be compressed upon the impact of the missile against a target and an electric fuze associated with the explosive charge of the missile; said piezoelectric elements being connected in series with said air gaps and said fuze so that initiation of said fuze occurs when the front part of said missile is deformed and one or both of said air gaps is short-circuited, a displaceable member located in one of said air gaps and mechanically connected to a manually operable control lever located outside of said missile for moving said member from a position where both of said air gaps are electrically insulating to a position where either of said air gaps is short-circuited. 

1. An electric fuze for an explosive missile having a trajectory safety device; a stand-off member projecting forwardly from said missile; said stand-off member comprising, an outer tubular member electrically and mechanically connected to an outer front closure plate forming an outer front surface of said missile; an inner tubular member located inside said outer tubular member but spaced apart and electrically insulated therefrom by an air gap; said inner tubular member being connected to an inner front closure plate located behind said outer front closure plate but spaced apart and electrically insulated therefrom by an air gap; said stand-off member being of less diameter than said front closure plate from which it projects, whereby said front closure plate forms a shoulder portion to said stand-off member; a set of piezoelectric elements located behind said inner front closure plate, and mounted to be compressed upon the impact of the missile against a target and an electric fuze associated with the explosive charge of the missile; said piezoelectric elements being connected in series with said air gaps and said fuze so that initiation of said fuze occurs when the front part of said missile is deformed and one or both of said air gaps is shortcircuited, a displaceable member located in one of said air gaps and mechanically connected to a manually operable control lever located outside of said missile for moving said member from a position where both of said air gaps are electrically insulating to a position where either of said air gaps is short-circuited. 